This invention relates to photocurable resin compositions for plastic molds and to plastic molds made therefrom.
Casings for electrical appliances for home use, electronic devices and communication apparatus, as well as machine parts are frequently made by molding various kinds of plastics. When such molded plastic objects are to be mass-produced, a small number of prototypes are preliminarily produced as a test. For producing such prototypes, and also for making final products if the total number to be produced is not too large, plastic molds are frequently made use of because they can be produced easily. This invention relates to photocurable resin compositions capable of producing such plastic molds directly by stereolithography, as well as plastic molds produced from such photocurable resin compositions by stereolithography.
General prior art methods of producing such plastic molds include the vacuum casting method using silicone resin, the resin transfer molding (RTM) method using unsaturated polyester resin, the hand lay-up method and the spray-up method. These prior art methods are disadvantageous in that they require much time and labor to produce plastic molds because a master model must be made first with a metal, wood, clay or plaster before the production of plastic molds. Indeed, very much labor and time are typically expended for the production of a plastic mold since frequent design changes are made during the production, because it is the very purpose of using plastic molds.
Attempts have also been made at stereo-lithography of photocurable resin compositions based on data inputted in a three-dimensional CAD, and various kinds of photocurable resin compositions for such a purpose have been proposed (for example, U.S. Pat. Nos. 4,942,066 and 5,002,855). These prior art photocurable resin compositions are not satisfactory, however, because thermal and mechanical properties of-the plastic molds obtained from them by stereolithography are not sufficiently acceptable and their durability is quite poor. Since the heat distortion temperature of plastic molds obtained from prior art photocurable resin compositions by stereolithography is lower than about 70.degree. C. and their tensile elastic modulus is less than about 8 GPa, the distortion and breakage of plastic molds are significant even when they are used for injection molding of general thermoplastics such as ABS resin such that production of even as few as only about 10-20 prototypes or products is not possible.